Hydrogen bromide
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| Names | |||
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| Preferred IUPAC name
Hydrogen bromide[citation needed]
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| Systematic IUPAC name
Bromane[1]
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| Identifiers | |||
10035-10-6  |
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| 3587158 | |||
| ChEBI | CHEBI:47266 |
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| ChEMBL | ChEMBL1231461  |
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| ChemSpider | 255 |
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| EC Number | 233-113-0 | ||
| Jmol 3D model | Interactive image | ||
| KEGG | C13645 |
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| MeSH | Hydrobromic+Acid | ||
| PubChem | 260 | ||
| RTECS number | MW3850000 | ||
| UN number | 1048 | ||
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| Properties | |||
| BrH | |||
| Molar mass | 80.91 g·mol−1 | ||
| Appearance | Colorless gas | ||
| Odor | Acrid | ||
| Density | 3.6452 kg/m3 (0 °C, 1013 mbar)[2] | ||
| Melting point | −86.9 °C (−124.4 °F; 186.2 K) | ||
| Boiling point | −66.8 °C (−88.2 °F; 206.3 K) | ||
| 221 g/100 mL (0 °C) 204 g/100 mL (15 °C) 193 g/100 mL (20 °C) 130 g/100 mL (100 °C) |
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| Solubility | soluble in alcohol, organic solvents | ||
| Vapor pressure | 2.308 MPa (at 21 °C) | ||
| Acidity (pKa) | ~–9[3] | ||
| Basicity (pKb) | ~23 | ||
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Refractive index (nD)
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1.325 | ||
| Structure | |||
| Linear | |||
| 820 mD | |||
| Thermochemistry | |||
| 350.7 mJ K−1 g−1 | |||
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Std molar
entropy (S |
198.696-198.704 J K−1 mol−1[4] | ||
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Std enthalpy of
formation (ΔfH |
-36.45--36.13 kJ mol−1[4] | ||
| Vapor pressure | {{{value}}} | ||
| Related compounds | |||
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Related compounds
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Hydrogen fluoride Hydrogen chloride Hydrogen iodide Hydrogen astatide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 verify (what is ?) |
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| Infobox references | |||
Hydrogen bromide is the diatomic molecule with the formula HBr. HBr is a colorless gas that condenses to a colorless liquid. Hydrobromic acid is a solution of HBr in water.
Contents
Solubility in water
HBr is very soluble in water, forming hydrobromic acid solution, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by weight form a constant-boiling azeotrope mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H2O until the constant boiling mixture composition is reached.
Uses of HBr
Hydrogen bromide and hydrobromic acid are important reagents in the production of inorganic and organic bromine compounds.[5] The free-radical addition of HBr to alkenes gives terminal alkyl bromides:
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- RCH=CH2 + HBr → RCH2–CH2Br
These alkylating agents are precursors to fatty amine derivatives. Similar free radical addition to allyl chloride and styrene gives 1-bromo-3-chloropropane and phenylethylbromide, respectively.
Hydrogen bromide reacts with dichloromethane to give bromochloromethane and dibromomethane, sequentially:
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- HBr + CH2Cl2 → HCl + CH2BrCl
- HBr + CH2BrCl → HCl + CH2Br2
Allyl bromide is prepared by treating allyl alcohol with HBr:
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- CH2=CHCH2OH + HBr → CH2=CHCH2Br + H2O
Other reactions
Although not widely used industrially, HBr adds to alkenes to give bromoalkanes, an important family of organobromine compounds. Similarly, HBr adds to haloalkene to form a geminal dihaloalkane. (This type of addition follows Markovnikov's rule):
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- RC(Br)=CH2 + HBr → RC(Br2)–CH3
HBr also adds to alkynes to yield bromoalkenes. The stereochemistry of this type of addition is usually anti:
- RC≡CH + HBr → RC(Br)=CH2
Also, HBr is used to open epoxides and lactones and in the synthesis of bromoacetals. Additionally, HBr catalyzes many organic reactions.[6][7][8][9]
Potential applications
HBr has been proposed for use in a utility-scale flow-type battery.[10]
Industrial preparation
Hydrogen bromide (along with hydrobromic acid) is produced by combining hydrogen and bromine at temperatures between 200-400 °C. The reaction is typically catalyzed by platinum or asbestos.[7][11]
Laboratory synthesis
HBr can be synthesized by a variety of methods. It may be prepared in the laboratory by distillation of a solution of sodium bromide or potassium bromide with phosphoric acid or diluted sulfuric acid:[12]
- 2 KBr + H2SO4 → K2SO4 + 2HBr
Concentrated sulfuric acid is ineffective because HBr formed will be oxidized to bromine gas:
- 2 HBr + H2SO4 → Br2 + SO2 + 2H2O
The acid may be prepared by several other methods, as well, including reaction of bromine either with phosphorus and water, or with sulfur and water:[12]
- 2 Br2 + S + 2 H2O → 4 HBr + SO2
Alternatively, it can be prepared by the bromination of tetraline:[12]
- C10H12 + 4 Br2 → C10H8Br4 + 4 HBr
Alternatively bromine can be reduced with phosphorous acid:[7]
- Br2 + H3PO3 + H2O → H3PO4 + 2 HBr
Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis of triphenylphosphonium bromide in refluxing xylene.[6]
Hydrogen bromide prepared by the above methods can be contaminated with Br2, which can be removed by passing the gas through a solution of phenol at room temperature in tetrachloromethane or other suitable solvent (producing 2,4,6-Tribromophenol and generating more HBr in the process) or through copper turnings at high temperature.[11]
Safety
HBr is highly corrosive and irritating to inhalation.
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Record in the GESTIS Substance Database of the IFA
- ↑ Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969.
- ↑ 4.0 4.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 6.0 6.1 Hercouet, A.;LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157-158.
- ↑ 7.0 7.1 7.2 Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809-812.
- ↑ Carlin, William W. U.S. Patent 4,147,601, April 3, 1979
- ↑ Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.
- ↑ http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535ag.pdf
- ↑ 11.0 11.1 Ruhoff, J. R.; Burnett, R. E.; Reid, E. E. "Hydrogen Bromide (Anhydrous)" Organic Syntheses, Vol. 15, p.35 (Coll. Vol. 2, p.338). (http://www.orgsyn.org/demo.aspx?prep=CV2P0338)
- ↑ 12.0 12.1 12.2 M. Schmeisser "Chlorine, Bromine, Iodine" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 282.
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